JP2010108841A - Fuel cell - Google Patents

Abstract

The present invention provides a fuel cell in which the concentration and dispersion of fuel supplied to each part of a fuel electrode of a fuel cell are controlled and output characteristics are improved.
A membrane electrode assembly (2) having a fuel electrode (13), an air electrode (16), and an electrolyte membrane (17) sandwiched between the fuel electrode (13) and the air electrode (16); the fuel of the membrane electrode assembly (2); A fuel distribution mechanism 4 disposed on the electrode 13 side and having a plurality of fuel discharge holes 22 for supplying fuel to the fuel electrode 13; and disposed between the membrane electrode assembly 2 and the fuel distribution mechanism 4. And a fuel diffusion layer 8 for diffusing the fuel discharged from the fuel distribution mechanism 4 and supplying it to the membrane electrode assembly 2, wherein the plurality of fuel discharge holes in the fuel distribution mechanism 4 The concentration and variation of the fuel supplied to the fuel electrode 13 are controlled by adjusting the hole interval L of 22 and the layer thickness T of the fuel diffusion layer 8.
[Selection] Figure 1

Description

  The present invention relates to a fuel cell using liquid fuel.

  In recent years, attempts have been made to use a fuel cell as a power source for portable electronic devices such as notebook computers and mobile phones so that they can be used for a long time without being charged. A fuel cell is characterized in that it can generate electric power simply by supplying fuel and air, and can generate electric power continuously for a long time if fuel is replenished. For this reason, if the fuel cell can be reduced in size, it can be said that the system is extremely advantageous as a power source for portable electronic devices.

  In particular, a direct methanol fuel cell (DMFC) is promising as a power source for portable electronic devices because it can be miniaturized and the fuel can be easily handled. As a liquid fuel supply method in the DMFC, an active method such as a gas supply type or a liquid supply type, or an internal vaporization type passive method in which the liquid fuel in the fuel container is vaporized inside the cell and supplied to the fuel electrode is known. ing.

  Among these, the internal vaporization type passive method is particularly advantageous for downsizing the DMFC. In the passive DMFC, for example, a structure is proposed in which a membrane electrode assembly (fuel cell) having a fuel electrode, an electrolyte membrane, and an air electrode is disposed on a fuel storage portion formed of a resin box-like container. However, when the fuel vaporized from the fuel container is directly supplied to the fuel cell, it is important to improve the output controllability of the fuel cell, but the current passive DMFC does not always have sufficient output controllability. Absent.

  For this reason, it has been studied to dispose a fuel distribution mechanism on the fuel electrode side of the fuel cell and distribute and supply the fuel to the fuel cell. The fuel distribution mechanism is, for example, a substantially plate-shaped fuel distribution having a fuel introduction hole for introducing liquid fuel and a plurality of fuel discharge holes connected to the fuel introduction hole via a thin tube and discharging the liquid fuel. It is supposed to consist of plates. Then, the fuel distribution mechanism and the fuel storage portion are connected by a flow path having a pump, and liquid fuel is supplied from the fuel storage portion to the fuel distribution mechanism, whereby liquid is discharged from the plurality of fuel discharge holes of the fuel distribution mechanism. The fuel can be discharged and supplied to the fuel cell.

At this time, the distribution and discharge amount of the liquid fuel discharged from the fuel distribution mechanism is controlled by adjusting the shape and diameter of the flow path, the liquid feeding capacity of the pump, the arrangement of the fuel discharge holes in the fuel distribution mechanism, and the like. The amount of fuel supplied to each part of the fuel cell can be made uniform, and the output characteristics of the fuel cell can be improved. In addition, for example, a resistance member made of a porous resin film or the like is disposed between the fuel battery cell and the fuel distribution mechanism as a fuel diffusion energy reducing means (see, for example, Patent Document 1).
JP 2008-2108030 A (see, for example, FIGS. 9 and 10)

  As described above, by using the fuel distribution mechanism, the amount of fuel supplied to each part of the fuel cell can be made uniform, and the output characteristics of the fuel cell can be improved. However, when viewed microscopically, the amount of fuel supplied in each part of the fuel cell is still different, and the concentration of fuel in each part varies.

  In addition, as described above, it has been studied to dispose the fuel diffusion energy reducing means between the fuel cell and the fuel distribution mechanism, but even if such a device is simply provided, each part of the fuel cell The variation in the fuel concentration cannot be sufficiently reduced, and the output characteristics of the fuel cell cannot necessarily be improved.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to provide a fuel cell in which the concentration and variation of the fuel supplied to each part of the fuel electrode are controlled and the output characteristics are improved. It is said.

  The fuel cell of the present invention includes a membrane electrode assembly having a fuel electrode, an air electrode, and an electrolyte membrane sandwiched between the fuel electrode and the air electrode; disposed on the fuel electrode side of the membrane electrode assembly And a fuel distribution mechanism having a plurality of fuel discharge holes for supplying fuel to the fuel electrode; fuel disposed between the membrane electrode assembly and the fuel distribution mechanism and discharged from the fuel distribution mechanism A fuel cell having a fuel diffusion layer that diffuses fuel and supplies the fuel electrode to the membrane electrode assembly, wherein the gap between the plurality of fuel discharge holes in the fuel distribution mechanism and the layer thickness of the fuel diffusion layer are adjusted Thus, the concentration and variation of the fuel supplied to the fuel electrode are controlled.

  It is preferable that the interval between the plurality of fuel discharge holes and the thickness of the fuel diffusion layer have a proportional relationship. In particular, the interval L [mm] between the plurality of fuel discharge holes and the layer thickness T [mm] of the fuel diffusion layer satisfy T = α × L (where α = 0.05 to 0.7). It is preferable to satisfy. The hole interval L between the plurality of fuel discharge holes and the layer thickness T of the fuel diffusion layer are determined such that the layer thickness T of the fuel diffusion layer is determined based on the hole interval L between the plurality of fuel discharge holes, for example. Alternatively, for example, the interval L between the plurality of fuel discharge holes may be determined based on the layer thickness T of the fuel diffusion layer.

  The diameter of the fuel discharge hole is preferably 0.05 mm or more and 1 mm or less. The fuel diffusion layer preferably has a porosity of 10% to 90%. The thermal conductivity of the fuel diffusion layer is preferably 0.03 W / (m · K) or more and 0.3 W / (m · K) or less.

  According to the present invention, by adjusting the hole spacing of the plurality of fuel discharge holes and the layer thickness of the fuel diffusion layer in the fuel distribution mechanism, the concentration and variation of the fuel supplied to each part of the fuel electrode can be controlled. The output characteristics of the fuel cell can be improved.

Hereinafter, embodiments for carrying out the present invention will be described with reference to the drawings.
First, the overall configuration of the fuel cell of the present invention will be described. FIG. 1 is a cross-sectional view showing the overall configuration of the fuel cell of the present invention. The fuel cell 1 is mainly composed of a fuel cell 2 constituting an electromotive unit and a fuel supply mechanism 3 for supplying fuel to the fuel cell 2. The fuel supply mechanism 3 includes, for example, a fuel distribution mechanism 4, a fuel storage section 5 that stores liquid fuel, a flow path 6 that connects the fuel distribution mechanism 4 and the fuel storage section 5, and the flow path 6. The pump 7 is mainly composed. In addition, a fuel diffusion layer 8 is disposed between the fuel cell 2 and the fuel distribution mechanism 4 so that the liquid fuel discharged from the fuel distribution mechanism 4 is diffused inside and supplied to the fuel cell 2.

  The fuel cell 2 includes an anode 13 which is a fuel electrode having an anode catalyst layer 11 and an anode gas diffusion layer 12, and a cathode 16 which is an air electrode or an oxidant electrode having a cathode catalyst layer 14 and a cathode gas diffusion layer 15. And a membrane electrode assembly (MEA) composed of a proton (hydrogen ion) conductive electrolyte membrane 17 sandwiched between the anode catalyst layer 11 and the cathode catalyst layer 14.

  Examples of the catalyst contained in the anode catalyst layer 11 and the cathode catalyst layer 14 include a simple substance of a platinum group element such as Pt, Ru, Rh, Ir, Os, and Pd, and an alloy containing the platinum group element. For the anode catalyst layer 11, it is preferable to use Pt—Ru, Pt—Mo, or the like having strong resistance to methanol, carbon monoxide, or the like. Pt, Pt—Ni or the like is preferably used for the cathode catalyst layer 14. However, the catalyst is not limited to these, and various substances having catalytic activity can be used. The catalyst may be either a supported catalyst using a conductive support such as a carbon material or an unsupported catalyst.

  Examples of the proton conductive material constituting the electrolyte membrane 17 include fluorine-based resins (Nafion (trade name, manufactured by DuPont) and Flemion (trade name, manufactured by Asahi Glass Co., Ltd.) such as a perfluorosulfonic acid polymer having a sulfonic acid group. Etc.), organic materials such as hydrocarbon resins having sulfonic acid groups, or inorganic materials such as tungstic acid and phosphotungstic acid. However, the proton conductive electrolyte membrane 17 is not limited to these.

  The anode gas diffusion layer 12 laminated on the anode catalyst layer 11 serves to uniformly supply fuel to the anode catalyst layer 11 and also serves as a current collector for the anode catalyst layer 11. The cathode gas diffusion layer 15 laminated on the cathode catalyst layer 14 serves to uniformly supply the oxidant to the cathode catalyst layer 14 and also serves as a current collector for the cathode catalyst layer 14. The anode gas diffusion layer 12 and the cathode gas diffusion layer 15 are made of a porous substrate.

  A conductive layer is laminated on the anode gas diffusion layer 12 and the cathode gas diffusion layer 15 as necessary. As these conductive layers, for example, a porous layer (for example, mesh) made of a conductive metal material such as Au or Ni, or a conductive metal material such as a foil, a thin film, or stainless steel (SUS), or a highly conductive material such as gold. A metal-coated composite material or the like is used. Rubber O-rings 19 are interposed between the electrolyte membrane 17 and the fuel distribution mechanism 4 and the cover plate 18, respectively, thereby preventing fuel leakage and oxidant leakage from the fuel cell 2. .

  Although not shown, the cover plate 18 has an opening for taking in air as an oxidant. A moisture retaining layer and a surface layer are disposed between the cover plate 18 and the cathode 16 as necessary. The moisturizing layer is impregnated with a part of the water generated in the cathode catalyst layer 14 to suppress the transpiration of water and promote uniform diffusion of air to the cathode catalyst layer 14. The surface layer adjusts the amount of air taken in, and has a plurality of air inlets whose number, size, etc. are adjusted according to the amount of air taken in.

  A fuel distribution mechanism 4 of the fuel supply mechanism 3 is arranged on the anode 13 side of the fuel battery cell 2 via the fuel diffusion layer 8. The fuel distribution mechanism 4 is connected to the fuel storage portion 5 via a liquid fuel flow path 6 such as a pipe, and the liquid fuel is introduced from the fuel storage section 5 into the fuel distribution mechanism 4 via the flow path 6. The flow path 6 is not limited to a pipe independent of the fuel distribution mechanism 4 or the fuel storage unit 5. For example, when the fuel distribution mechanism 4 and the fuel storage unit 5 are stacked and integrated, the liquid fuel that connects them is used. It may be a flow path.

  Liquid fuel corresponding to the fuel cells 2 is stored in the fuel storage portion 5. Examples of the liquid fuel include methanol fuels such as aqueous methanol solutions of various concentrations and pure methanol. The liquid fuel is not necessarily limited to methanol fuel. The liquid fuel may be, for example, an ethanol fuel such as an ethanol aqueous solution or pure ethanol, a propanol fuel such as a propanol aqueous solution or pure propanol, a glycol fuel such as a glycol aqueous solution or pure glycol, dimethyl ether, formic acid, or other liquid fuel. In any case, liquid fuel corresponding to the fuel battery cell 2 is stored in the fuel storage portion 5.

  The pump 7 is not a circulation pump that circulates fuel, but is a fuel supply pump that sends liquid fuel from the fuel storage unit 5 to the fuel distribution mechanism 4 to the last. By supplying liquid fuel when necessary with such a pump 7, the controllability of the fuel supply amount can be improved. Since the fuel cell 1 does not circulate the fuel, it is different from the conventional active method and does not impair the downsizing of the apparatus. Further, since the pump 7 is used for supplying the liquid fuel and is different from a pure passive system such as a conventional internal vaporization type, it is called, for example, a semi-passive type.

  The type of the pump 7 is not particularly limited, but a rotary vane pump, an electroosmotic flow pump, a diaphragm pump, from the viewpoint that a small amount of liquid fuel can be sent with good controllability and can be reduced in size and weight. It is preferable to use an ironing pump or the like. A rotary vane pump feeds liquid by rotating a wing with a motor. The electroosmotic flow pump uses a sintered porous material such as silica that causes an electroosmotic flow phenomenon. The diaphragm pump is a pump that feeds liquid by driving the diaphragm with an electromagnet or piezoelectric ceramics. The squeezing pump presses a part of the flexible fuel flow path and squeezes the fuel. Among these, it is more preferable to use an electroosmotic pump or a diaphragm pump having piezoelectric ceramics from the viewpoint of driving power, size, and the like.

  Since the main object of the fuel cell 1 is a small electronic device, the liquid feeding capacity of the pump 7 is preferably in the range of 10 μL / min to 1 mL / min. When the liquid feeding capacity exceeds 1 mL / min, the amount of liquid fuel fed at a time becomes too large, and the stop time of the pump 7 occupying the entire operation period becomes long. For this reason, fluctuations in the amount of fuel supplied to the fuel cells 2 increase, and as a result, fluctuations in output increase. A reservoir for preventing this may be provided between the pump 7 and the fuel distribution mechanism 4, but even if such a configuration is applied, fluctuations in the fuel supply amount cannot be sufficiently suppressed. This will increase the size of the device.

  On the other hand, when the liquid feeding capacity of the pump 7 is less than 10 μL / min, there is a risk that the supply capacity will be insufficient when the amount of fuel consumption increases when the apparatus is started up. As a result, the starting characteristics of the fuel cell 1 are deteriorated. From such a point, it is preferable to use the pump 7 having a liquid feeding capacity in the range of 10 μL / min to 1 mL / min. The liquid feeding capacity of the pump 7 is more preferably in the range of 10 to 200 μL / min. In order to stably realize such a liquid feeding amount, it is preferable to apply an electroosmotic flow pump or a diaphragm pump to the pump 7.

  For example, as shown in FIG. 2, the fuel distribution mechanism 4 includes at least one fuel introduction hole 21 for introducing liquid fuel, a plurality of fuel discharge holes 22 for discharging liquid fuel, and the fuel introduction holes 21. And a fuel distribution plate 24 having a narrow tube 23 connecting the fuel discharge hole 22.

  The plurality of fuel discharge holes 22 are evenly spaced over substantially the entire main surface of the fuel distribution plate 24 so that variations in the concentration of fuel supplied to each part of the anode 13 serving as the fuel electrode are reduced. Has been placed. The narrow tube 23 is branched into a plurality of portions along the way, and a fuel discharge hole 22 is provided at each terminal portion of the branched thin tube 23. The liquid fuel is introduced from the fuel introduction hole 21, led to the plurality of fuel discharge holes 22 through the thin tubes 23, and supplied from the plurality of fuel discharge holes 22 to the anode 13 through the fuel diffusion layer 8.

  According to such a fuel distribution mechanism 4, the amount of fuel supplied to each part of the anode 13 can be made uniform, a power generation reaction can be efficiently generated, and output characteristics can be improved. In particular, by connecting the fuel introduction hole 21 and the fuel discharge hole 22 with the thin tube 23, liquid fuel can be evenly discharged from the fuel discharge hole 22 regardless of the direction and position of the fuel discharge hole 22 with respect to the fuel introduction hole 21. Can do.

  The fuel diffusion layer 8 is disposed between the fuel distribution mechanism 4 and the anode 13. Specifically, the fuel distribution mechanism 4 is disposed so as to be embedded in a rectangular recess provided in a substantially central portion. The fuel diffusion layer 8 temporarily absorbs the liquid fuel discharged from the fuel distribution mechanism 4 and diffuses the absorbed liquid fuel in the surface direction to thereby supply the fuel supplied to each part of the anode 13. Can be made uniform, and variations in fuel concentration can be reduced.

  As such a fuel diffusion layer 8, any material that can diffuse the liquid fuel discharged from the fuel distribution mechanism 4 may be used. For example, a porous resin film is preferably used. The porosity of the fuel diffusion layer 8 is preferably in the range of 10 to 90%. When the porosity of the fuel diffusion layer 8 is less than 10%, the number of pores is too small, and the fuel supplied to the anode 13 through the fuel diffusion layer 8 is reduced, and sufficient output characteristics may not be obtained. There is. On the other hand, when the porosity of the fuel diffusion layer 8 exceeds 90%, there are too many pores, so that the liquid fuel discharged from the fuel distribution mechanism 4 cannot be sufficiently diffused in the plane direction by capillary action, and the anode There is a possibility that the variation in the concentration of the fuel supplied to each part of 13 cannot be reduced. The porosity of the fuel diffusion layer 8 is preferably in the range of 20 to 60%.

  The thermal conductivity of the fuel diffusion layer 8 is preferably 0.03 W / (m · K) or more and 0.3 W / (m · K) or less. When the thermal conductivity of the fuel diffusion layer 8 is less than 0.03 W / (m · K), the heat generated by the power generation of the fuel cell 2 cannot be released, and the temperature of the fuel cell 2 is excessive. May rise. On the other hand, when the thermal conductivity of the fuel diffusion layer 8 exceeds 0.3 W / (m · K), the heat generated in the fuel cell 2 easily escapes to the outside through the fuel diffusion layer 8. The temperature of 8 is not sufficient to diffuse the liquid fuel, and the liquid fuel discharged from the fuel distribution mechanism 4 may not be sufficiently diffused in the surface direction. By setting the thermal conductivity of the fuel diffusion layer 8 within the above range, the temperature of the fuel diffusion layer 8 can be appropriately increased, and thus the liquid fuel discharged from the fuel distribution mechanism 4 can be sufficiently discharged in the plane direction. Can be diffused.

  In such a fuel cell 1, the liquid fuel discharged from the fuel distribution mechanism 4 is supplied to the anode 13 through the fuel diffusion layer 8. Further, the fuel supplied to the anode 13 diffuses through the anode gas diffusion layer 12 and is supplied to the anode catalyst layer 11.

When methanol fuel is used as the liquid fuel, the internal reforming reaction of methanol shown in the following formula (1) proceeds in the anode catalyst layer 11. When pure methanol is used as the methanol fuel, the water produced in the cathode catalyst layer 14 or the water in the electrolyte membrane 17 is reacted with methanol to cause the internal reforming reaction of the formula (1), or The internal reforming reaction is caused by another reaction mechanism that does not require water.
_{CH 3 OH + H 2 O →} CO 2 + 6H + + 6e - ... (1)

Electrons (e ⁻ ) generated by this reaction are guided to the outside through a current collector, and are operated to a cathode 16 after operating a portable electronic device or the like as so-called electricity. Further, (1) a proton (H ⁺⁾ generated by the internal reforming reaction of the formula is introduced to the cathode 16 via the electrolyte membrane 17. Since air is supplied to the cathode 16 as an oxidant, electrons (e ⁻ ) and protons (H ⁺ ) that have reached the cathode 16 are oxygen in the cathode catalyst layer 14 and the following formula (2): And water is produced with this reaction.
6e ⁻ + 6H ⁺ + (3/2) O ₂ → 3H ₂ O (2)

Next, the main part of the present invention will be described.
In the present invention, for example, by adjusting the hole interval L of the plurality of fuel discharge holes 22 in the fuel distribution mechanism 4 as shown in FIG. 2 and the layer thickness T of the fuel diffusion layer 8 as shown in FIG. It is characterized by controlling the concentration and variation of the fuel supplied to each part of 13. In the following description, the concentration of fuel supplied to each part of the anode 13 is simply referred to as fuel concentration, and the variation in each part of the anode 13 of the fuel concentration is simply referred to as variation in fuel concentration or simply as variation. .

  By providing the fuel distribution mechanism 4 and the fuel diffusion layer 8 as described above, it is possible to reduce the variation in the fuel concentration compared to the case where such a device is not provided. However, when viewed microscopically, the fuel concentration still varies. Even if the variation in the fuel concentration can be reduced, if the fuel concentration becomes low, the output characteristics of the fuel cell 1 deteriorate, which is not preferable.

  In the present invention, the fuel concentration and its variation are controlled by adjusting the hole interval L of the plurality of fuel discharge holes 22 in the fuel distribution mechanism 4 and the layer thickness T of the fuel diffusion layer 8, and in particular the fuel concentration. As a result, the output characteristics of the fuel cell 1 can be improved by narrowing the variation range while increasing the overall size. In the following description, the hole interval L of the plurality of fuel discharge holes 22 in the fuel distribution mechanism 4 is simply referred to as the hole interval L, and the layer thickness T of the fuel diffusion layer 8 is simply referred to as the layer thickness T. .

  Specifically, when the hole interval L is wide, by increasing the layer thickness T, the liquid fuel discharged from the fuel discharge hole 22 can be sufficiently diffused in the plane direction inside the fuel diffusion layer 8, As a result, variations in fuel concentration can be reduced. On the other hand, when the hole interval L is narrow, it is not always necessary to diffuse the liquid fuel discharged from the fuel discharge hole 22 in the plane direction inside the fuel diffusion layer 8, and thus the layer thickness T can be reduced. Further, by reducing the layer thickness T in this way, the fuel concentration can be increased as a whole.

  It is preferable that the hole interval L [mm] and the layer thickness T [mm] have a proportional relationship, and it is particularly preferable to have a proportional relationship as shown in the following formula (1).

T = α × L (1)
(However, α = 0.05 to 0.7)

  By having such a proportional relationship, the variation can be narrowed while increasing the fuel concentration as a whole, and as a result, the output characteristics of the fuel cell 1 can be improved.

  That is, when the layer thickness T is smaller than 0.05L as shown in the formula (1), the layer thickness T is not sufficient with respect to the hole interval L, so that the liquid fuel discharged from the fuel discharge hole 22 is faced. There is a possibility that the fuel concentration cannot be sufficiently reduced due to insufficient diffusion in the direction.

  Further, when the layer thickness T is larger than 0.7 L, the layer thickness T is excessively thick with respect to the hole interval L, so that the liquid fuel discharged from the fuel discharge hole 22 sufficiently passes through the fuel diffusion layer 8. The fuel concentration is lowered, and there is a possibility that sufficient output characteristics cannot be obtained. In the formula (1), α is more preferably 0.1 to 0.6 from the viewpoint of further reducing the variation while further increasing the fuel concentration as a whole.

  In addition, as for the hole interval L and the layer thickness T, the other may be determined on the basis, for example, the layer thickness T may be determined on the basis of the hole interval L according to the above formula (1), For example, the hole interval L may be determined based on the layer thickness T.

  The hole interval L is preferably 0.1 mm or more and 10 mm or less. If the hole interval L exceeds 10 mm, even if the layer thickness T is increased, the fuel concentration variation may not be reduced. Further, when the layer thickness T is increased in order to reduce the variation in the fuel concentration, the liquid fuel discharged from the fuel discharge hole 22 cannot sufficiently pass through the fuel diffusion layer 8, so that the fuel concentration decreases. There is a possibility that sufficient output characteristics cannot be obtained.

  On the other hand, if the hole interval L is less than 0.1 mm, the liquid fuel discharged from the fuel discharge hole 22 can be easily diffused uniformly in the plane direction inside the fuel diffusion layer 8, but the number of the fuel discharge holes 22 is excessive. May increase, and the manufacturability of the fuel distribution mechanism 4 may be reduced. For example, as shown in FIG. 2, the hole interval L is the shortest distance from the edge of the fuel discharge hole 22 to the edge of the fuel discharge hole 22 adjacent to the fuel discharge hole 22.

  Moreover, it is preferable that the hole diameter of the fuel discharge hole 22 is 0.05 mm or more and 1 mm or less. If the hole diameter of the fuel discharge hole 22 is less than 0.05 mm, the liquid fuel may not be sufficiently discharged. On the other hand, if the hole diameter of the fuel discharge hole 22 exceeds 1 mm, the liquid fuel discharge amount may not be appropriately controlled.

  Furthermore, the layer thickness T is preferably 0.1 mm or more and 3 mm or less. When the layer thickness T is less than 0.1 mm, the layer thickness T is too thin, so that the liquid fuel discharged from the fuel discharge hole 22 cannot be sufficiently diffused in the surface direction, and the variation in fuel concentration increases. There is a fear. When the layer thickness T exceeds 3 mm, the layer thickness T is too thick, so that the liquid fuel discharged from the fuel discharge hole 22 cannot sufficiently pass through the fuel diffusion layer 8 and the fuel concentration decreases. There is a possibility that sufficient output characteristics cannot be obtained.

In the present invention, the fuel concentration at a position on the main surface of the fuel diffusion layer 8 on the fuel distribution mechanism 4 side is defined as C _in, and the fuel concentration on the main surface on the anode 13 side of the fuel diffusion layer 8 corresponding to this position. When the concentration is C _out and these ratios (C _out / C _in × 100) are the concentration ratio, the average value of the concentration ratios (C _out / C _in × 100) obtained at a plurality of positions of the fuel diffusion layer 8 Is preferably 25% or more. At this time, the difference between the maximum value and the minimum value in the plurality of concentration ratios is preferably 50% or less.

Here, the fuel concentrations C _in and C _out are indicated by the amount of fuel [mol / m ³ ] contained per unit volume in the pores of the fuel diffusion layer 8. Moreover, the several position for calculating | requiring the average value of density | concentration ratio can be made into arbitrary dozens of places, for example.

  The average value of the concentration ratio is an index that represents the overall fuel concentration, that is, the concentration of fuel supplied to each part of the anode 13. When the average value of the concentration ratio is high, the fuel concentration, that is, the concentration of the fuel supplied to each part of the anode 13 is generally high, and as a result, sufficient output characteristics can be easily obtained. As described above, by adjusting the hole interval L and the layer thickness T, specifically, by adjusting the hole interval L and the layer thickness T so as to satisfy the above formula (1), the average of the concentration ratios The value can be increased to 25% or more, and as a result, sufficient output characteristics can be easily obtained. The average value of the concentration ratio is more preferably 30% or more, and further preferably 40% or more.

  Further, the difference between the maximum value and the minimum value of the concentration ratio serves as an index representing the range of the concentration ratio variation, that is, the range of the fuel concentration variation. When the difference between the maximum value and the minimum value of the concentration ratio is small, the variation in the concentration ratio, that is, the variation in the fuel concentration is small, and as a result, sufficient output characteristics can be easily obtained. As described above, by adjusting the hole interval L and the layer thickness T, specifically, by adjusting the hole interval L and the layer thickness T so as to satisfy the above formula (1), the maximum concentration ratio can be obtained. The difference between the value and the minimum value can be reduced to 50% or less, and as a result, sufficient output characteristics can be easily obtained. The difference between the maximum value and the minimum value of the concentration ratio is more preferably 40% or less.

Hereinafter, the present invention will be described more specifically with reference to examples.
A fuel cell 1 as shown in FIG. 1 is used to generate power by changing the gap L between the fuel discharge holes 22 of the fuel distribution mechanism 4 and the layer thickness T of the fuel diffusion layer 8 as shown in FIG. The average value of the concentration ratio was determined. Note that the average value of the concentration ratio is the fuel concentration C _in on the main surface on the fuel distribution mechanism 4 side in any 10 locations of the fuel diffusion layer 8 and the corresponding fuel concentration C _in the main surface on the anode 13 side. _out, and the concentration ratio (C _out / C _in × 100) _in each part was determined from these, and these were averaged.

  In addition, the fuel distribution mechanism 4 uses three types in which the gap L between the fuel discharge holes 22 is 1 mm, 3 mm, or 5 mm, and the fuel discharge hole 22 has a diameter of 0.08 to 0.4 mm. The number of discharge holes 22 was 128, and the amount of fuel supplied was 15 μl / min. On the other hand, as the fuel diffusion layer 8, four kinds of layers having a layer thickness T of 0.2 mm, 0.5 mm, 1 mm, or 2 mm are used, all having a porosity of 26% and a thermal conductivity of 0.15 to 0. .25 W / (m · K). Furthermore, the area of the fuel cell 2 was about 40 mm × 80 mm, and pure methanol was used as the liquid fuel to generate power at a constant voltage of 0.35V.

  The results are shown in FIGS. 3 to 5 show the results for each interval L of the fuel discharge hole 22, and the average value of the concentration ratio is indicated by a black circle. In addition, in FIGS. 3 to 5, the range of the maximum value and the minimum value of the concentration ratio is shown by vertical lines together with the average value of the concentration ratio.

  As shown in FIGS. 3 to 5, the layer thickness T of the fuel diffusion layer 8 is set within a range of 0.05 to 0.7 times the hole interval L of the fuel discharge holes 22 as shown in the formula (1). It can be seen that the average value of the concentration ratio can be increased to 25% or more, and the difference between the maximum value and the minimum value of the concentration ratio can be decreased to 50% or less.

  That is, as shown in FIG. 3, when the gap L between the fuel discharge holes 22 is 1 mm, the layer thickness T of the fuel diffusion layer 8 is 0.2 mm (α = T / L = 0.2). The average value of the density ratio can be 40% or more, and the difference between the maximum value and the minimum value of the density ratio can be about 50%. Further, by setting the layer thickness T of the fuel diffusion layer 8 to 0.5 mm (α = T / L = 0.5), the maximum value and the minimum value of the concentration ratio are maintained while the average value of the concentration ratio is about 30%. And about 20%.

  Further, as shown in FIG. 4, the layer thickness T of the fuel diffusion layer 8 is set to 0.5 mm (α = T / L = 0.17) even when the hole interval L between the fuel discharge holes 22 is 3 mm. Thus, the average value of the density ratio can be about 40%, and the difference between the maximum value and the minimum value of the density ratio can be about 50%. Further, by setting the layer thickness T of the fuel diffusion layer 8 to 1 mm (α = T / L = 0.3), the average value of the concentration ratio is about 40%, and the maximum value and the minimum value of the concentration ratio are The difference can be 20% or less.

  Furthermore, as shown in FIG. 5, even when the hole interval L between the fuel discharge holes 22 is 5 mm, by setting the layer thickness T of the fuel diffusion layer 8 to 1 mm (α = T / L = 0.2), The average value of the density ratio can be about 35%, and the difference between the maximum value and the minimum value of the density ratio can be about 30%. Further, by setting the layer thickness T of the fuel diffusion layer 8 to 2 mm (α = T / L = 0.4), the average value of the concentration ratio is about 30%, and the maximum value and the minimum value of the concentration ratio are The difference can be about 10%.

  Although the fuel cell of the present invention has been described above, the present invention is not limited to the above-described embodiment itself, and can be embodied by modifying constituent elements without departing from the scope of the invention in the implementation stage. In addition, various inventions can be formed by appropriately combining a plurality of components disclosed in the embodiment. Furthermore, some components may be deleted from all the components shown in the above embodiment.

  For example, the pump 7 is preferably provided in the flow path 6 that connects the fuel distribution mechanism 4 and the fuel storage unit 5, but such a pump 7 is not necessarily provided. In the fuel distribution mechanism 4, it is preferable that the fuel introduction hole 21 and the fuel discharge hole 22 are connected by a thin tube 23. For example, the fuel distribution mechanism 4 is box-shaped, and substantially the entire interior thereof. Alternatively, the air gap may be used as a liquid fuel flow path connecting the fuel introduction hole 21 and the fuel discharge hole 22. Further, the fuel supplied to the membrane electrode assembly may be all supplied with fuel vapor, but the present invention can be applied even when a part of the fuel is supplied in a liquid state.

Sectional drawing which shows an example of the fuel cell of this invention. The top view which shows an example of a fuel distribution mechanism. The figure which shows the relationship between the layer thickness of a fuel diffusion layer when the hole space | interval of a fuel discharge hole is 1 mm, the average value of density | concentration ratio, and the maximum and minimum value. The figure which shows the relationship between the layer thickness of a fuel diffusion layer when the hole space | interval of a fuel discharge hole is 3 mm, the average value of density | concentration ratio, and the maximum and minimum value. The figure which shows the relationship between the layer thickness of a fuel diffusion layer when the hole space | interval of a fuel discharge hole is 5 mm, the average value of density | concentration ratio, and the maximum and minimum value.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Fuel cell, 2 ... Fuel cell, 3 ... Fuel supply mechanism, 4 ... Fuel distribution mechanism, 5 ... Fuel accommodating part, 6 ... Flow path, 7 ... Pump, 8 ... Fuel diffusion layer, 11 ... Anode catalyst layer, DESCRIPTION OF SYMBOLS 12 ... Anode gas diffusion layer, 13 ... Anode (fuel electrode) 14 ... Cathode catalyst layer, 15 ... Cathode gas diffusion layer, 16 ... Cathode (air electrode / oxidant electrode), 17 ... Electrolyte membrane, 21 ... Fuel introduction hole, 22 ... Fuel discharge hole, 23 ... Narrow tube, 24 ... Fuel distribution plate, H ... Layer thickness of fuel diffusion layer, L ... Hole spacing of fuel discharge hole

Claims (8)

A membrane electrode assembly having a fuel electrode, an air electrode, and an electrolyte membrane sandwiched between the fuel electrode and the air electrode; disposed on the fuel electrode side of the membrane electrode assembly; A fuel distribution mechanism having a plurality of fuel discharge holes for supplying fuel; and disposed between the membrane electrode assembly and the fuel distribution mechanism, the fuel discharged from the fuel distribution mechanism is diffused to diffuse the membrane electrode A fuel cell having a fuel diffusion layer supplied to the assembly,
The concentration and variation of the fuel supplied to the fuel electrode are controlled by adjusting the hole spacing of the plurality of fuel discharge holes in the fuel distribution mechanism and the layer thickness of the fuel diffusion layer. Fuel cell.   The fuel cell according to claim 1, wherein a hole interval between the plurality of fuel discharge holes and a layer thickness of the fuel diffusion layer have a proportional relationship. The interval L [mm] between the plurality of fuel discharge holes and the layer thickness T [mm] of the fuel diffusion layer are as follows:
T = α × L
(However, α = 0.05 to 0.7)
The fuel cell according to claim 2, wherein:   The fuel cell according to claim 3, wherein a layer thickness T of the fuel diffusion layer is determined based on a hole interval L of the plurality of fuel discharge holes.   The fuel cell according to claim 3, wherein a hole interval L between the plurality of fuel discharge holes is determined based on a layer thickness T of the fuel diffusion layer.   The fuel cell according to any one of claims 1 to 5, wherein a hole diameter of the fuel discharge hole is 0.05 mm or more and 1 mm or less.   The fuel cell according to any one of claims 1 to 6, wherein the porosity of the fuel diffusion layer is 10% or more and 90% or less.   8. The fuel according to claim 1, wherein the thermal conductivity of the fuel diffusion layer is 0.03 W / (m · K) or more and 0.3 W / (m · K) or less. battery.

Images